The present invention relates to electromagnetic valve actuators which may be used for actuating a cylinder valve, for example, of an internal combustion engine of vehicles, by mainly using an electromagnetic force.
Such electromagnetic valve actuators have been disclosed in U.S. Pat. Nos. 5,799,630 and 4,779,582. The former of the conventional techniques includes a disk-like armature fixed to an intake valve of an engine, and valve-closing and valve-opening electromagnets that attract the armature for moving the intake valve to the closed and full open positions. There are provided a valve-closing spring for biasing the armature in such a direction as to move the intake valve toward the closed position and a valve-opening spring for biasing the armature in such a direction as to move the intake valve toward the full open position. Each electromagnet is connected to an electronic control unit that controls an energizing current for the electromagnet depending on operating conditions of the engine. The intake valve is operated to move to the closed and full open positions and held therein by association of the spring forces of the springs and the attractive forces of the electromagnets alternately energized. The latter of the conventional techniques includes a housing made of a magnetic material, an armature connected with an intake valve of an engine and moveably disposed within the housing, and a pair of compressed springs biasing the armature for retaining the valve in a neutral position between closed and full open positions of the valve. The armature has an H-shape and includes a sleeve portion extending along the center axis of the armature. A pair of electromagnets are disposed in such a manner that the armature is interposed therebetween. An annular permanent magnet is provided for holding the armature in the respective closed and full open position. The electromagnets include upper and lower cores having lower and upper faces opposed to the sleeve portion of the armature. The electromagnets include upper and lower coils that are wound around the cores and disposed on upper and lower faces of the permanent magnet, respectively. When the valve is placed in the respective closed and full open position, each coil is activated with a current therethrough to cancel the magnetic field of the permanent magnetic pole and allow the spring to move the valve member toward the other position. Thus, the motion of the valve is shifted by alternate energization of the coils.
However, in the actuator described in the former, upon the valve being moved between the closed and full open positions, the electromagnets are alternately activated with a current to attract the armature against the spring force of the springs. The valve is held in the closed or full open position by continuous energization of the electromagnet. This causes an increased consumption of electrical energy, resulting in undesirable increase in engine load and fuel consumption. In the actuator of the latter, the coils of the electromagnets are not connected in series and independently cooperate with the corresponding core to generate an opposing magnetic field relative to the magnetic field of the permanent magnet upon being energized for the cancellation of the magnetic field of the permanent magnet. The magnetic circuit is formed in which the magnetic flux passes through the core, the housing, the north pole of the permanent magnet and the south pole thereof, and the armature and returns to the core. The magnetic flux of the electromagnet thus passes through the permanent magnet in the direction reverse to the magnetic flux of the permanent magnet. Therefore, the permanent magnet is influenced by the opposing magnetic field relative to the permanent magnet and thus tends to be demagnetized. This will lead to considerable reduction of the durability of the permanent magnet. Further, since resistance in the magnetic circuit will be increased due to the passage of the magnetic flux through the permanent magnet in the reverse direction, the electric energy consumption required for the cancellation of the magnetic field of the permanent magnet will become greater.